Conventionally, in a wheel rolling bearing unit of this type, there is known a wheel rolling bearing unit in which a metallic cover member which is formed by pressing a low carbon steel sheet is fitted in a one end side opening of an outer ring of a rolling bearing so as to close the same opening in order to protect an interior of the rolling bearing which is assembled to an outer circumference of a hub shaft of a hub wheel from muddy water or dust.
In addition, the cover member has integrally a lid portion and a cylindrical portion which is caused to project in an axial direction from an outer circumferential edge of the lid portion, and an outside diameter of the cylindrical portion is set in such a manner as to be slightly larger than an inside diameter dimension of the one end side opening of the outer ring. In addition, it has been general practice that the cover member is fitted (press fitted) in the one end side opening of the outer ring at the cylindrical portion thereof for attachment.
In addition, in wheel rolling bearing units, as a wheel rolling bearing unit in which a one end side opening of an outer ring thereof is closed by a cover member, a wheel rolling bearing unit is disclosed in, for example, JP63-A-176761.